The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some of such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
In wireless communication environment it is typical that the propagating conditions of radio signals vary constantly. A receiver experiences a constant variation, i.e. fading, in the signal level of transmitted signals. The radio channel is changing constantly due to fading and multipath effects, handset movement, for example.
In recent years, the use of multiple antennas in the transmitter and/or receiver which results in so called multiple-input-single-output (MISO) single-input-multiple-output (SIMO) or multiple-input-multiple-output (MIMO) radio channel has been widely studied. The use of multiple antennas may offer improved capacity and significant potential for improved reliability compared to single antenna systems. In addition, MIMO transmissions may be used to provide multi-user MIMO (MU-MIMO) communications where an access node generates multiple spatially separate communication beams and each beam is used to communicate with a subset of terminal devices of the wireless network of the access node.